1. Field of the Invention
The present invention relates to a circuit element for influencing pulses having two series-connected inductances which connect a first input terminal to a first output terminal, and having a first capacitor which is connected between the connection point of the inductances and the second terminals, the second terminals being either directly connected to one another or coincide with one another.
2. Description of the Prior Art
In complex data processing networks, in particular, it is occasionally necessary to delay pulses by electric time delay elements. Time delay elements of this type can be constructed, as is well known in the art, by four-terminal networks composed of coils and capacitors. In one such circuit, the series arm of the four-terminal network, i.e. between an input terminal and an output terminal, there is a series arrangement of two inductances. The shunt arm of the network is formed by a capacitor which is connected, on the one hand, to the junction of the two inductances and, on the other hand, to a direct link between a second input terminal and a second output terminal. The second input terminal and the second output terminal are not only electrically identical, but, in practice, frequently coincide and are provided as a single terminal. In order to steepen the edges of the pulses which are to be delayed, the inductances are often designed so that they are inductively coupled to each other. In addition, they can also be shunted by a second capacitor. In order to improve the pulse characteristic of the network, it is also known to connect a plurality of time delay elements, having correspondingly shorter delay times, in series, instead of achieving the desired delay time by a suitable dimensioning of a single delay network.
In other cases, it is necessary to flatten the pulse edges. Pulses having very steep edges can, in fact, give rise to undesirable disturbances. This happens, for example, when such pulses are transmitted simultaneously from a transmitting station over a main line, which is terminated correctly in respect of load impedance, to a plurality of receiving stations which are connected by way of nonterminated tap lines to the main line. As is known, a flattening of pulse edges can be achieved with low pass filters. However, it is necessary to accept a certain signal delay which, in most cases, is undesirable. A low pass filter differs from the delay element discussed above by virtue of the omission of the second-mentioned shunt capacitor and the absence, or at least substantial reduction, of the mutual coupling of the two inductances.
Time delay elements for signal delays in the order of a few nanoseconds are commercially available. A plurality of independent time delay elements having different delay times, e.g. 2, 4, 6 and 8 ns are accommodated in a single module in order to be able to select, as required, delay times of between 2 and 20 ns in steps of 2 ns. In these known time delay elements, the series inductances are formed by wound coils having a central tap. A design of this type is not only expensive but also occupies a relatively large amount of space.